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Owing to the inherent instability caused by the low Cu(I)/Cu(0) half-cell reduction potential, Cu(0)-containing copper nanoclusters are quite uncommon in comparison to their Ag and Au congeners. Here, a novel eight-electron superatomic copper nanocluster [Cu 31 (4-MeO-PhC≡C) 21 (dppe) 3 ](ClO 4 ) 2 ( Cu 31 , dppe = 1,2-bis(diphenylphosphino)ethane) is presented with total structural characterization. The structural determination reveals that Cu 31 features an inherent chiral metal core arising from the helical arrangement of two sets of three Cu 2 units encircling the icosahedral Cu 13 core, which is further shielded by 4-MeO-PhC≡C - and dppe ligands. Cu 31 is the first copper nanocluster carrying eight free electrons, which is further corroborated by electrospray ionization mass spectrometry, X-ray photoelectron spectroscopy and density functional theory calculations. Interestingly, Cu 31 demonstrates the first near-infrared (750-950 nm, NIR-I) window absorption and the second near-infrared (1000-1700 nm, NIR-II) window emission, which is exceptional in the copper nanocluster family and endows it with great potential in biological applications. Of note, the 4-methoxy groups providing close contacts with neighboring clusters are crucial for the cluster formation and crystallization, while 2-methoxyphenylacetylene leads only to copper hydride clusters, Cu 6 H or Cu 32 H 14 . This research not only showcases a new member of copper superatoms but also exemplifies that copper nanoclusters, which are nonluminous in the visible range may emit luminescence in the deep NIR region.

The first mixed-valence nanocluster Cu I /Cu II with the highest percentage of Cu II ions was synthesized by using 4- tert -butylcalix[4]arene (Calix4), with the formula DMF 2 ⊂[(CO 3 ) 2- @Cu II 6 Cu I 3 (Calix4) 3 Cl 2 (DMF) 5 (H 3 O)]•DMF ( 1 ), as a photothermal nanocluster. Its structure was characterized using single-crystal X-ray diffraction, Fourier-transform infrared spectroscopy, and powder X-ray diffraction. In addition, the charge state and chemical composition of the nanocluster were determined using electrospray ionization spectrometry and X-ray photoelectron spectroscopy (XPS) spectrum. The results of the XPS and X-ray crystallography revealed that there are two independent Cu II and Cu I centers in nanocluster 1 with the relative abundances of 66.6 and 33.3% for Cu II and Cu I , respectively. The nanocluster contains three four-coordinated Cu I ions with a square-planar geometry and six five-coordinated Cu II ions with a square pyramid geometry. The nanocluster shows strong near-infrared optical absorption in the solid state and excellent photothermal conversion ability (the equilibrium temperature ∼78.2 °C) with the light absorption centers in 286-917 nm over previous reported pentanucleus Cu I 4 Cu II clusters and Cu II compounds.

An atomically resolved gold nanocluster Au 99 (C≡CC 6 H 3 -2,4-F 2 ) 40 ( Au 99 ) with an unusual 59 valence electrons has been synthesized. Single-crystal X-ray diffraction reveals that its Au 79 kernel is a Au 49 Marks decahedron capped by two Au 15 units. The surface structure of Au 99 consists of 20 linear Au(C≡CR) 2 staples. Intercluster interactions are observed between these D 5 symmetric clusters. The existence of an unpaired electron is verified by magnetic measurement. Interestingly, this open-shell gold cluster Au 99 stays intact in toluene solution at 80 °C for more than a week, and it has good charging-discharging capability under electrochemical conditions. The compact ligand shell protection around the symmetric core accounts for the high stability. This work suggests that geometric factors may play a crucial role in determining the stability of a metal nanocluster, even though the cluster has an open-shell electronic structure.

The boundary between molecular and metallic gold nanoclusters is of special interest. The difficulty in obtaining atomically precise nanoclusters larger than 2 nm limits the determination of such a boundary. The synthesis and total structural determination of the largest all-alkynyl-protected gold nanocluster (Ph 4 P) 6 [Au 156 (C≡CR) 60 ] (R = 4-CF 3 C 6 H 4 -) ( Au 156 ) are reported. It presents an ideal platform for studying the relationship between the structure and the metallic nature. Au 156 has a rod shape with the length and width of the kernel being 2.38 and 2.04 nm, respectively. The cluster contains a concentric Au 126 core structure (Au 46 @Au 50 @Au 30 ) protected by 30 linear RC≡C-Au-C≡CR staple motifs. It is interesting that Au 156 displays multiple excitonic peaks in the steady-state absorption spectrum (molecular) and pump-power-dependent excited-state dynamics as revealed in the transient absorption spectrum (metallic), which indicates that Au 156 is a critical crossover cluster for the transition from molecular to metallic state. Au 156 is the smallest-sized gold nanocluster showing metal-like electron dynamics, and it is recognized that the cluster shape is one of the important factors determining the molecular or metallic nature of a gold nanocluster.

We report the controlled synthesis and structures of two isomeric gold nanoclusters, whose compositions are determined to be Au 23 (C≡CBu t ) 15 (denoted as Au 23 -1 and Au 23 -2 ) by single-crystal X-ray diffraction and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. This is the first time isomerism is discovered in alkynyl-protected gold nanoclusters. The metal-to-ligand ratios in these two clusters are different from known Au n (SR) m systems and have not been observed in the Au x (C≡CPh) y family. This pair of isomers exhibits different optical properties, although they have similar structures and identical components. For both Au 23 clusters, time-dependent density functional theory calculations revealed the frontier orbitals highest occupied molecular orbital (HOMO)-1, HOMO, and lowest unoccupied molecular orbital (LUMO) are mainly constructed from the Au 15 kernel and V-shaped alkynyl-gold motifs. The HOMO → LUMO transition of Au 23 -1 is optically forbidden, whereas it is allowed in Au 23 -2 . It is also found that Au 23 -2 cluster can be transformed to Au 23 -1 spontaneously under ambient conditions. This work offers further insight into the synthesis and isomerism of all-alkynyl-protected gold nanoclusters and will stimulate more investigation of isomeric metal nanoclusters.

A pair of enantiopure Au 13 nanoclusters have been enantioselectively synthesized by chiral ligands with stereogenic centers at the phosphorus atoms. Their structures are determined by X-ray crystallography, which are typical models with a high symmetric core and chiral surface ligand arrangement. Correlation between the crystallographic structure, the calculation, and the circular dichroism (CD) study indicates that helical ligand arrangement inducing the core into chiral distortion accounts for the chiroptical activities in the visible region. A rare example of cocrystallization of a mixture of diastereomers has been observed for the first time for gold nanoclusters, reflecting the lack of chiral self-sorting of the ligands.

A 64-nuclearity silver cluster encapsulating a unique POM anion [Mn(III)Mn(IV)2Mo14O56](17-) has been synthesized. The formation of the templating core performs a reassembly process for increasing nuclearities from {MnMo9} to {Mn3Mo14}. It represents a rare inorganic meso anion containing mixed-valent Mn that is built up by d-{Mn(IV)Mo7} and l-{Mn(IV)Mo7} units connecting together through a {Mn(III)} fragment.

We report the total structure determination of a large bimetallic nanocluster with an overall composition of [Au80Ag30(C≡CPh)42Cl9]Cl. It is the largest structurally characterized bimetallic coinage nanocluster so far. The 110 metal atoms are distributed in a concentric four-shell Russian doll arrangement, Au6@Au35@Ag30Au18@Au21. There are 42 PhC≡C- ligands and 9 μ2-chloride ligands clamping on the cluster surface. The chloride is proven to be critical for the formation of this giant cluster, as the control experiment in the absence of halide gives only smaller species. This work demonstrates that the halide can play a key role in the formation of a large metal nanocluster, and the halide effect should be considered in the design and synthesis of metal nanoclusters.

The activation of C(sp(3))-H bonds is challenging, due to their high bond dissociation energy, low proton acidity, and highly nonpolar character. Herein we report a unique gold(I)-silver(I) oxo cluster protected by hemilabile phosphine ligands [OAu3Ag3(PPhpy2)3](BF4)4 (1), which can activate C(sp(3))-H bonds under mild conditions for a broad scope of methyl ketones (RCOCH3, R = methyl, phenyl, 2-methylphenyl, 2-aminophenyl, 2-hydroxylphenyl, 2-pyridyl, 2-thiazolyl, tert-butyl, ethyl, isopropyl). Activation happens via triple deprotonation of the methyl group, leading to formation of heterometallic Au(I)-Ag(I) clusters with formula RCOCAu4Ag4(PPhpy2)4(BF4)5 (PPhpy2 = bis(2-pyridyl)phenylphosphine). Cluster 1 can be generated in situ via the reaction of [OAu3Ag(PPhpy2)3](BF4)2 with 2 equiv of AgBF4. The oxo ion and the metal centers are found to be essential in the cleavage of sp(3) C-H bonds of methyl ketones. Interestingly, cluster 1 selectively activates the C-H bonds in -CH3 rather than the N-H bonds in -NH2 or the O-H bond in -OH which is traditionally thought to be more reactive than C-H bonds. Control experiments with butanone, 3-methylbutanone, and cyclopentanone as substrates show that the auration of the C-H bond of the terminal methyl group is preferred over secondary or tertiary sp(3) C-H bonds; in other words, the C-H bond activation is influenced by steric effect. This work highlights the powerful reactivity of metal clusters toward C-H activation and sheds new light on gold(I)-mediated catalysis.